1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Description of the Related Art
In recent years, liquid crystal display devices are widely used as information display devices for portable devices. In order to reduce the size of the portable devices, the liquid crystal display devices need to be reduced in entire thickness.
However, the liquid crystal display device is not self-luminous, and hence a planar lighting unit called “backlight” is often required. It is known that the liquid crystal display device used for portable devices employs a kind of planar lighting unit with a light source allocated on a side surface of a light guide panel in order that the thickness of the backlight can be reduced. In such planar lighting unit, the light guide panel has an appropriate structure for scattering incident light from the side surface to the front surface thereof uniformly. Further, in the planar lighting unit, there must be given a consideration to the avoidance of undesired light from being reflected on a screen.
For example, JP 07-43710 A discloses a liquid crystal display device, in which a light guide panel is provided with a plurality of grooves on a surface thereof, the plurality of grooves each having projections projecting outward on both sides of the aperture of the groove. According to the invention disclosed in JP 07-43710 A, light which has entered the projections goes outside to be diffusely reflected by a reflective member, and then enters the light guide panel again.
Meanwhile, JP 2005-251687 A discloses a liquid crystal display device, in which light sources are provided on a side surface of a light guide panel, and a light blocking member is provided on a flexible printed circuit board so as to prevent a color of the flexible printed circuit board from being mixed with colors on a screen.
In general, a light guide panel is made of a transparent thermoplastic resin, such as polycarbonate or polymethylmethacrylate, and is formed through projection molding. However, when the projection molding method is employed, it has been difficult to obtain a light guide plate with a thickness smaller than a certain degree, for example, the thickness of 1 mm or less, due to the reason that the resin is insufficiently filled into the mold or it is difficult to remove the finished product from the mold.